Whether it's clear or color you still need to "baby" it over thin clear. As far as the temp reducers and hardeners, darn tootin that will make a difference. You really should have the faster reducers and hardeners. HOWEVER, and this is a big HOWEVER, those slower reducers and hardeners are the best ones even in the colder weather for doing something like this frame. It's hard to keep from getting dry spots on something like this. If you have a little "wetter" reducer and hardener (slower flashing/activating) you can keep it wet over the whole thing until you are done shooting.
But IF and I am not saying you do for sure have thin spots in the clear, just a guestimate, you would want the faster flashing solvents so they don't soak in and lift.
Listen, if you can get the thing warm, and then just don't bomb it on, you should be ok. Did you see the propane heater discussion a while ago?