Welcome to the forum!
That sounds pretty good! What does the three year warranty cover? I'd be looking at the cost of the insurance versus what it covers and how handy you are if you need to make any repairs. Before signing any papers, really take your time and do a complete examination of the trailer and look in every nook and cranny you can find. Run the AC and heat. Check the water heater. Look underneath. If the warranty covers all appliances and operating systems including labor and parts, that would make the deal very good.
Good luck, and I hope your enjoying a camper very soon!