I'm working on specing/quoting for a job and I'm trying to decide the best way to make the mould. As usual, it has to be as cheap as possible. The job is to make 4-6 (maybe more later) simple rectangle crates - 5 sided, open top (or to be closed just with a bit of ply or flat sheet) gel coat finish on the outside. The finish doesn't have to be great as they're only for floating a pontoon on, I just need enough of a finish to ensure easy releases.
I will probably just make a simple mdf female mould for this. I just need to decide on the best way to seal it. As I said it will only need to handle half a dozen pulls, so what do you think. My choices are down to epoxy coating resin, epoxy tooling gel coat, both of the previous, pattern coat gloss, or (as I'll be buying it anyway for the parts) would polyester resin do the job?