I picked up some stuff today pretty cheaply it's a rubber latex which can be poured can I use this instead of RTV and can it be thinned/give good results thinking of using it for tarps/ammo cans ect

Woodland scenics has a rubber latex product and I have used it instead of RTV. It works pretty well. I don't know your specific product, but I would recommend extra layers if you know you're going to pour resin in it. The heat will reduce the life of a thin mold.
I'm used to brushing my stuff on and this makes it difficult to control the sides of the mold, so I would recommend planning it out carefully beforehand.

Some kind of container or base would help. clay or something similar might work