Lovely work.
I do have the answer to your issue....quote from your posting is in italics
"The foam is covered with vinyl. For whatever reason the vinyl over foam has been problematic - I have had to re-glue several pieces. (I used marine vinyl and both 3M spray adhesive and DAP brush on contact cement- this may be part of the problem.)"
This issue was caused by using standard marine vinyl, the kind you find in fabric stores. The issue was not the adhesive, it was the material itself. That material is for upholstery work where it is secured by sewing or by fasteners such as staples. It is not a product that will stay secured with adhesives. No fault of yours other than not knowing in advance that that this particular material is not adhesive friendly. I made the same error but fortunately on only a small area. Then when it came down I went to a local upholstery shop that specializes in boats and they taught me that all vinyls are not suitable for installation with adhesives and that includes the widely available "marine vinyl".
There are vinyls that can be glued using contact cement which is a good choice as that old stand by yellow contact cement that comes in a can is heat resistant. But those vinyls are not available in your local fabric stores. They need to be special ordered from upholstery sources that cater to automotive or marine suppliers. But remember not all "marine" vinyl can be glued so you have to specify to the sales clerks that you need a special vinyl for that purpose. The adhesive friendly vinyls have a layer of somewhat fuzzy fabric on the reverse side. That layer is what makes them work with the adhesives, that textured fabric layer grips into the adhesives.
This is the link to a supplier who ships nationwide.
http://www.miamicorp.com/ That is where I got my vinyl from. They are a reliable and friendly company to deal with. Before you click to buy on the internet do call them on the phone and talk to them about your choice of what you have seen on their website to double check if it is the right product for your specific application. That is worth taking the time to do as you don't want to waste time and money on something you think might work versus something that has been verified to work.
It cost considerably less to order it from online sources than ordering from a middle man upholstery shop. However you can look through the fabric sample books at those shops to help you narrow your choices. You can also request samples from the online sources. There is typically a fee for that sample plus the cost of shipping.