Doc - I'd check the sticker on your trailer again. I'm thinking it's rated at 2990 pounds since you didn't mention that the trailer had brakes. It probably has a 3500# axle and tire ratings to that amount but once a trailer rating goes over 3000#, in most states, brakes are required.
Since you're crossing state lines, you'll want to be as strapped down as you can. Each state may have different requirements so you'll want to be as good as the most stringent state.
I'd set the tongue weight to about 300# (10% of the towed load).
Your trailer probably weighs between 1000 & 1300# so you're going to be right at the 3000# limit.
I've used the gate to load my RTV a few times. If you have angle iron under the tires when you drive up, you should be OK. If tires will be on the mesh, I'd put a 2x8 or larger on the ramp as already discussed. Personally, I don't driving with the gate up, even if it is mesh. At minimum, I'd take a ratchet strap and go from the top of the ramp (when it's in the upright, locked position) and run that strap up the trailer a ways and connect the other end to a vertical upright on the trailer. I can't stand hearing that thing rattle...
Oh, and I do the chains around the front and rear drawbars like others have already mentioned. I don't tie vehicles down anywhere above the suspension (e.g. a strap across the floor or through the grill guard). When you hit a bump, your suspension moves thus giving the straps/chains some slack but then immediately after, a big hit when it comes back). That's not good for the vehicle or the tie down material (especially if it's straps).