I just noticed EU is mentioned a lot in GregTech and rubber trees exist, but have no utility beyond being wood, as it seems, so it seems to want IC2. I tend to prefer small packs and play mods in their pure form, but if GT is mostly intended for use with at least IC2(and fastcraft) I should add it.
GT rubber trees can have a resin hole you can pull a sticky resin from ( no tap, just hands ), or slap a resin bag on to auto collect them. Then it needs either squeezed or centrifuged to get latex and that needs put in the coagulator to get rubber. I keep IC2exp around still for the crop sticks and auto farm. And nano/quantum armor will be nice to make one of these days, though you now have to visit the end to do it.