> ... 3m 77 which actually works quite well ...
I like the 30 sec. to 15 minute bonding window it claims to have. For my overspray issue, I can spray outside my studio and have time to haul the pieces inside for putting them together. It's the need to get that assembly right the first time that bothers me the most about the contact adhesives.
For silver prints I always used a heat mount print. But for the individual photographer/printer, I doubt the capital costs of the hardware to handle 40x60's could be spread adequately. In some museum shows we've had Samy's do that end of the business, but there are real advantages to having as much of the process be doable in-house as possible.
> ... epoxy’s ... won’t stand the test of time ..
as they will crack and or discolor plus x-gas forever. All epoxy yellows with UV exposure, as far as I can tell. I'm not sure the extent of that risk for inside display, where the epoxy is under the canvas, and that has also been sprayed with (somewhat) UV blocking Print Shield spray. Would the color ever affect the image?
For coatings, the non-yellowing aliphatic polyurethanes are much better for our purposes. They also have more elasticity.
The modern 100% solids versions of these with, supposedly, no VOC's might be something I'll have try. I'm not sure what odor issues those have.
(Speaking of which, the odors of some inkjet canvas products that are not well aged are rather off-putting. I never thought bad smells would be a factor in my "paper" selection.)
Paul