I totally agree with you on Feb-Mar being the best riding time. Half the time I drive three hours (one way) to ride, and the extra hour or two of daylight sure makes it a lot easier to get in a full day of riding without having to get up early and drive both ways in the dark, dodging the dawn/dusk deer rush. Between that and the chance of tearing up a sled, it takes a solid start to be worth it to me to ride in Dec. I have an idea (and most of the parts) to build a fan-cooled beater sled to hopefully open up the shoulder season without risking my main ride, but then if you're on a budget, you're probably still better off building more time at the peak of the season anyway.
I've got a sled deck - it's steel and weighs a ton (well, half a ton anyway), and after the pain of loading and unloading it several times a season (half the time just to haul one sled) I got wise and bought a folding ramp and just haul my sled in the bed of the truck. The deck has no advantage with just one sled, and I burn 20-30% more diesel with it on. When it comes to hauling two sleds, I'd lean toward a deck over a trailer, but if I had it to do over I'd want aluminum. There's less to go wrong with a deck, you get more traction with the weight over the axle, and it's easier to get around. Obviously at some point you need a trailer, and I've been in a few that I'd love to have, but it's a big budget-buster, and sometimes the roads are "fun" enough without 10k lbs. behind you. If I had money to burn, I'd still buy one; be nice to have even if you ended up leaving it behind half the time. Just like sleds, if you have the money and space, you'll build a quiver consisting of a deck and a couple trailers, but most of us have to make do with some sort of compromise.