I personally think the XCR resin is an excellent product for skinning pieces. I don't skin that much pieces because I prefer using moulds and resin infusion or prepreg, but when skinning pieces XCR is the best resin I've tried so far. Never had problems with it so far. Just need to be sure to mix it well and use it in the correct conditions like on the TDS. 
Most important thing is to use it in a stable environment, so avoid having big temperature changes. 

If you need to use heat lamps on top of your part isn't mostly a good sign in best conditions you have your part in a room with very low humidity and constant temperatures (part and resin) at around 23°C the entire cure. meaning not just while it is curing and feeling hard but full 48 hours. 
before sanding it, make sure the resin is "fully cured" not just "feeling hard". I let my parts cure for 72 hours after last pour and even postcure them till 55°C to avoid having the mistakes above. 
by all the above I'm not saying you cant use this resin in your garage or shed with a heater on the part, but it will make it harder