<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-09-30</periodOfReport>
    <issuer>
        <issuerCik>0000763744</issuerCik>
        <issuerName>DREW INDUSTRIES INCORPORATED</issuerName>
        <issuerTradingSymbol>DW</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001059270</rptOwnerCik>
            <rptOwnerName>ROSE EDWARD R III</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>500 CRESCENT COURT</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 250</rptOwnerStreet2>
            <rptOwnerCity>DALLAS</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75201</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>1</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><derivativeTable><derivativeTransaction><securityTitle><value>Deferred Stock Units</value></securityTitle><conversionOrExercisePrice><value>0</value></conversionOrExercisePrice><transactionDate><value>2003-09-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>821.43</value></transactionShares><transactionPricePerShare><value>18.20</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2004-12-17</value></exerciseDate><expirationDate><value>2004-12-17</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>821.43</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>31584.27</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeTransaction><securityTitle><value>Deferred Stock Units</value></securityTitle><conversionOrExercisePrice><value>0</value></conversionOrExercisePrice><transactionDate><value>2003-09-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>63.36</value></transactionShares><transactionPricePerShare><value>18.15</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2004-12-17</value></exerciseDate><expirationDate><value>2004-12-17</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>63.36</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>31647.63</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeTransaction><securityTitle><value>Deferred Stock Units</value></securityTitle><conversionOrExercisePrice><value>0</value></conversionOrExercisePrice><transactionDate><value>2003-09-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>63.89</value></transactionShares><transactionPricePerShare><value>18.00</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2004-12-17</value></exerciseDate><expirationDate><value>2004-12-17</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>63.89</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>31711.52</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeTransaction><securityTitle><value>Deferred Stock Units</value></securityTitle><conversionOrExercisePrice><value>0</value></conversionOrExercisePrice><transactionDate><value>2003-09-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>127.85</value></transactionShares><transactionPricePerShare><value>17.99</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2004-12-17</value></exerciseDate><expirationDate><value>2004-12-17</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>127.85</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>31839.37</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">Included in this amount is 25,000 Stock Options, with the remainder consisting of Deferred Stock Units.</footnote></footnotes><remarks/><ownerSignature><signatureName>Fredric M. Zinn on behalf of Edward W. Rose III</signatureName><signatureDate>2003-09-30</signatureDate></ownerSignature></ownershipDocument>

