You've been given some great advice and I'll add my two pennies worth. 1. Buy a removable pingle chock for the front wheel and 2. Buy at least 4 good stainless eyebolts and secure them thru the floor and prefereably thru the frame of the trailer if at all possible. Been there and done that and I'll be looking for a trailer myself to take the bike here and there when need be and also for general use to take the garden tractor in for service etc. Here in FL, you can pretty much buy a brand new trailer starting at around $900 on up. As another poster mentioned, used trailers can be to say the least an adventure once you've gotten it home. Bearing buddies are an absolute must on any trailer IMHO. Got them on my boat trailer and have had em on every trailer I've owned.

BM

 

first, I would not get one with a a tall ramp tailgate they catches lots of wind and on a long trip will hurt your mpg. second, if you get a open trailer look at the floor if it made of wood normally 2X6 planks make sure they are bolted to the frame and in good condition. 2500lb axle would be fine with a 2 inch coupler. two reasons i say this. 2500lb axle will have 14 or 15 inch wheels. dont go with smaller wheels and is useful later to haul bricks or anything heavy. I like a 3500lb axle myself. third, if you use a 2 inch ball so do most other people and other trailers. if i come to visit and need the trailer i need it to have a 2inch coupler or i will have use your receiver spike and will most likely forget to return it. trust me lost two this way. fourth, now back to the floor most small utility trailers have a lip in the rear but not in the front to retain the planks. so if the planks are not screwed to the frame and you strap it to apoint on the floor, i prefer the rail system, the whole bike could bounce out. in my enclosed trailer i use the rail system but the floor is bolted down and designed for this system or for d-ring tie down points. fourth, this brings up the suspension system of the trailer a cheaper trailer will have leaf springs which are fine but they do bounce when you hit a bump a big bump can bounce off the ground. i prefer a torsion bar type axle which twists for suspension and does not bounce near as bad. and this type of axle allows the triler to set lower to the ground. the last thing is something i wish i would looked for on my enclosed trailer. stabilizer jacks in the rear, they are just legs that drop down in the back and you lock them in and adjust the height. they do not lift the trailer but you can load and unload your bike without it being hooked to the truck (make sure the wheels are chalked so the trailer does not go anywhere.) its easy to dent your tailgate if you forget to lock the coupler trust me my dad hooked mine up once and it cost my 200 bucks to fix. by the way he thought it was funny and reminded me when i was about 10 i sharped all of his new screwdrivers on the side walk about a hour after he bought them. also if you are looking around try to get one with mess sides later on it may get stuff from sliding out.
if its used repack bearing always repack bearing on aused trialer. and get bearing buddies if you are unsure about the size just take the dust cover into autozone and ask for help. use a good quality grease i like marine waterproff since i use it on my boat too.
lights are easy to replace and cost less than 40 bucks wire and all. if you need a jack or new coupler get bulldog brand. i like pivoting jacks so i can swing them out of the way and not drag them if i hit a dip. also if you get one that has the screw down jack in the middle of the coupler with the handle on the top make sure you screw it completely up tight and check it when you stop. on a long trip vibration and gravity will let it lower itself. just look at lots of trialers and see how many have bent jacks. this is why i replace mine with the pivoting one.
last get a spare mount it or strap it down where it can bounce into your bike. make sure you carry a lug wrech which will fit thelugs on your trailer wheels. i use a have moon style drive on jack to change a tire but if your truck uses a screw jack that you can get really flat(most do) you will be fine but practice it before you get on the road. at least twice a year normally once int eh summer and once in the fall i have to stop and loan my jack and 4-way lug wrench to someone on the roadside. but hey i sold my spare once to guy on the way to the lake. told him he could just barrow it and leave me something (like his really hot girlfriend in the bikini) until he returned it. i think he was just in hurry to get the girl out on his boat.
hope this helps if you need me to explain any of this just pm me on here.
have good vaca