Auto number for quotes & invoices

Auto number for quotes & invoices

Process flow for our sales team.  
1) Create quote and obtain signature on quote
2) When ready to turn over to production, "Convert to Invoice"

Problem
I have set up auto number for Quotes and Invoices.  I set both to start at "600100".  I have "Mapped Custom Fields" so that the fields match in both Quotes and Invoices.
All Quotes are not turned into invoices.  So, I may have 100 Quotes generated and only 10 are converted to "Invoices".
I get to 600200 for Quotes and I am at 600110 for Invoices.
My " Invoices auto numbers" are out of sync and do not match the Quote numbers.
Any ideas on how to address this?  I need the quote number to be consistent through the lifecycle from Quote to Invoice.

Please help.  This is a very big problem for my organization.
Thank you.
Trent
VP Sales