The best tip I can give is.....just to get your hands dirty with the stuff. (actually, on that note, always use gloves. I didn't for the first couple batches and I just about killed myself having to take an Acetone bath up to my shoulders). I personally use West System Epoxy and Smooth Cast 305 for my Epoxy resin and casting resin respectively. Now where you get this kind of stuff in the UK, I don't know but....whatever you do end up using, just experiment a little bit by mixing up batches of this or that as per the directions (don't 'practice' on your actual model), test out what rubber RTV does, and generally get some hands on experience. Once you do that, you'll probably have more specific questions if any at all. I found that the stuff isn't difficult to work with. Messy, yes....difficult....no. If you can count to 5 (5:1 mix ratio of resin/hardener for the Epoxy I use. 1:1 for the casting resin), you should be able to handle it. Confidence in using it comes quickly. (If you saw on my build thread my Epoxy dispenser that I bought from Aircraft Spruce, I can not speak highly enough for that thing....worth it's weight in gold when it comes to handling Epoxy. I'm sure it's paid for itself in no waste, no mess).
That's the best I can do for you. At some point, you're going to have to get up to your elbows in goo. .......you'll see what I mean.
"I don't have anything else planned for this afternoon." - Lt. Col J.O.E. Vandeleur
A Bridge Too Far (1977)