I've been searching through the threads looking for a place to ask my questions.....and I've found your post with a totally different need , but one I have dealt with recently !!!
I donated some sepia paintings (sketches) which were acrylic on unprimed calico....they are 6' x 4'...and I thought "just a bit of fun".....But I have had a framing company phone me asking how best to conserve these works as they are about to frame some of them !!!!!! LOL !
I kept one which didn't reach the reserve of $1000 Au.
!!!!!!!....so I had a 'go' at sealing and varnishing it... experimentally.
After trying several different products....I have concluded the best results by far are from a product made by an Aussie company . I can give you its name ...but I figure if I give you the product description you will be able to find a suitable similar product.
It is a POLYMER GLOSS VARNISH....(A PURE ACRYLIC RESIN SUSPENDED IN WATER)......(it has several uses including as a glue in mixed media)
When used as a varnish it needs to be pre-diluted with water ...and it dries to a tough pliable water-resistant film.
IMO...It is the best thing on material I have yet found ....and it doesn't dry glossy ! ( it is easily folded or rolled etc , and feels just a little firmer than my thin calico, but not much at all !)
BTW...I don't like its very glossy results on my well-prepped , gessoed and well-finished fine art acrylic paintings....Way too glossy !!!!
I hope this is of some help to you !!! I love what you are doing , and sounds like so much fun as well !