Trailer for 18' seacraft

[rayhawk]

Hi guys, I am getting a new trailer for my 1978 18' seacraft. I had a tandem setup that I am replacing, but am unsure of the appropriate weight rating I should get on the axles. The standard tandem setup is 4000lb capacity. Does anybody see any issues with this? I figure the boat must weigh around 2500, but that is just an estimate, never had it weighed. I am running a Mercury 150hp carb V6 and a 54 gallon tank. Any idea if I am close on the weight, and either way, is this too much trailer? Should I get 1500lb springs instead (3000lb total)? I like the idea of having some extra capacity but don't want to get so carried away as to have an unsafe rig. Oh and here is a pic of my boat.