I'm in Melbourne Australia and am assembling a V2.5 ROV and I'm very excited!
I have some experience with 2 part resins and casting of small parts but have been struggling to find Hysol E-90 here in Australia (no surprises there) but have been able to locate one or 2 possible alternatives in the epoxy area of resins etc. One possibility would be West System r105 Resin with the H206 Slow hardener, it is a marine epoxy with low viscosity and it is quite widely available around Australia. I have not tested this yet but plan to do so over the upcoming month or so.
In my investigations I have spoken to various manufacturers and chemical bonding suppliers and most have said the same thing: in their opinion the Epoxy bonding will NOT form a proper 'chemical' bond with the acrylic layer material. This is probably ok initially but with each use there will be some flex in the end caps and wiring and this may eventually result in the plug/potting having a hairline crack from the endcap and small water leaks.
I am intending to do some tests with an acrylic casting resin (usually for jewellery and craft), which should form a firm chemical bond with the acrylic of the end cap and solve this issue.
There will not be as much flex in the final material but I think a stiffener may be able to be added to the wire loom to prevent work hardening of the cores. This material is often used to pour around delicate objects like insects, and should be ideal for getting in and around the wiring harness. It also sets water clear allowing some inspection of the loom if required. It should also expand and contract at the same rate with temperature changes as the rest of the endcap assembly.
If anyone has any tips or suggestions or thoughts on the above regarding the choice of casting materials I would be keen to hear, I will of course let know know how my testing goes with the different alternatives.
Sorry for the long post.