1
                                                                    EXHIBIT 10.3




                            As of September 28, 1999



Morgan Stanley & Co. Incorporated
1585 Broadway
New York, New York 10036
(as Representative
of the Underwriters)

Ambac Assurance Corporation
One State Street Plaza
New York, New York  10004

         Re:      Advanta Revolving Home Equity Loan Trust 1999-B
                  Underwriting Agreement and Insurance Agreement

Ladies and Gentlemen:

         Pursuant to the Underwriting Agreement dated September 21, 1999 (the
"Underwriting Agreement") between Advanta Conduit Receivables, Inc. (the
"Sponsor" or "ACRI") and Morgan Stanley & Co. Incorporated, as representative of
the underwriters named therein (the "Underwriters"), and the Insurance and
Indemnity Agreement dated September 28, 1999 (the "Insurance Agreement" and
together with the Underwriting Agreement, the "Designated Agreements") among the
Sponsor, Advanta Mortgage Corp. USA, Advanta Revolving Home Equity Loan Trust
1999-B and Ambac Assurance Corporation (the "Insurer"), ACRI has undertaken
certain financial obligations with respect to the indemnification of the
Underwriters and of the Insurer with respect to the Registration Statement, the
Prospectus and the Prospectus Supplement described in the Designated Agreements.
Any financial obligations of ACRI under the Designated Agreements, whether or
not specifically enumerated in this paragraph, are hereinafter referred to as
the "Joint and Several Obligations"; provided, however, that "Joint and Several
Obligations" shall mean only the financial obligations of ACRI under the
Designated Agreements (including the payment of money damages for a breach of
any of ACRI's obligations under the Designated Agreements, whether financial or
otherwise) but shall not include any obligations not relating to the payment of
money.

         As a condition of their respective executions of the Underwriting
Agreement and of the Insurance Agreement, the Underwriters and the Insurer have
required the undersigned, Advanta Mortgage Holding Company ("AMHC"), the
indirect parent corporation of ACRI, to acknowledge its joint-and-several
liability with ACRI for the payment of the Joint and Several Obligations under
the Designated Agreements.

         Now, therefore, the Underwriter, the Insurer and AMHC do hereby agree
that:



                                       4
   2
                  AMHC hereby agrees to be absolutely and unconditionally
                  jointly and severally liable with ACRI to the Underwriters for
                  the payment of the Joint and Several Obligations under the
                  Underwriting Agreement.

                  AHMC hereby agrees to be absolutely and unconditionally and
                  jointly and severally liable with ACRI to the Insurer for
                  payment of the Joint and Several Obligations under the
                  Insurance Agreement.

                  AMHC may honor its obligations hereunder either by direct
                  payment of any Joint and Several Obligations or by causing any
                  Joint and Several Obligations to be paid to the Underwriters
                  or to the Insurer, by ACRI or another affiliate of AMHC.

         Capitalized terms used herein and not defined herein shall have their
respective meanings set forth in the Designated Agreements.

         This letter and the respective obligations and rights hereunder and
thereunder shall not be delegated or assigned by you without the prior written
consent of the Insurer. This letter may not be amended or otherwise modified
except pursuant to a writing signed by each of the parties hereto. This letter
may be executed by the signatories hereto in several counterparts, each of which
shall be deemed to be an original and all of which shall constitute one and the
same letter.

         THIS LETTER SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE
LAWS OF THE STATE OF NEW YORK. EACH OF THE UNDERSIGNED PARTIES HEREBY KNOWINGLY,
VOLUNTARILY AND INTENTIONALLY WAIVES ANY RIGHTS IT MAY HAVE TO A TRIAL BY JURY
IN RESPECT OF ANY LITIGATION BASED HEREON, OR ARISING OUT OF OR IN CONNECTION
WITH, THIS LETTER, AND ANY OTHER COURSE OF CONDUCT, COURSE OF DEALING,
STATEMENTS (WHETHER ORAL OR WRITTEN) OR ACTIONS OF ANY OF THE UNDERSIGNED
PARTIES IN CONNECTION HEREWITH OR THEREWITH.




                                       5
   3
         Capitalized terms used herein and not defined herein shall have their
respective meanings as set forth in the Designated Agreement.

                                        Very truly yours,

                                        ADVANTA MORTGAGE HOLDING
                                             COMPANY



                                        By:
                                              -----------------------------
                                              Authorized Signatory


CONFIRMED AND ACCEPTED,
as of the date first above written:

AMBAC ASSURANCE CORPORATION


By:
      -----------------------------
      Authorized Signatory



MORGAN STANLEY & CO. INCORPORATED


By:
      -----------------------------
      Authorized Signatory




                                       6