Very few (read just a handful) of production builders "epoxy" stuff down to stringers. Some do use a Plexus style of adhesive to bond liners, soles, etc., but generally bonding as previously described, was done with polyester and vinylester based adhesive mixtures, not epoxy. Only recently have epoxies made serious inroads into the production builders market.
I find concrete blocks are much better than car batteries, as weights. They weigh about 35 - 37 pounds each, are uniform in size, easy to stack, don't leak anything, can be rolled onto any side, etc. I literally have a stack of them for just this purpose, outside the shop.
PL works in small craft, but not especially in large craft and doesn't tolerate dynamic loading very well. I have pictures of bulkheads, that have been skinned with PL as the adhesive, the 1/2" skins sheared their glue lines in a year, on one 34' power cruiser I repaired. Clean glue line failures in all examples.
If you want to "bed" the deck, consider a polyurethane or a polysulfide as mechanically fasten the deck down. 3M-5200 is pretty aggressive and likely stringer damage will occur if the deck eventually get pulled, so maybe a less aggressive adhesive, like 3M-4000 or 3M-101 (my choice) I too would suggest you're doing a good job, as moisture does seem to work up, from the stringer faying surface, into substrate above and naturally the stringer below. The light cloth will help greatly in preventing this.
