Good luck on the long cruises. You will visit a lot of rest areas. To get the kinks/aches out.
I made the seat in my bucket from foam purchased at the local fabric shop. Real med density rubber for 2 1/2" and 1 1/2" regular poly foam to form the upper pattern of the seat. Then covered with pleated 1/2" foam/vinyl. This was covered on a plywood base with seat belt webbing in the "butt" areas. 2" foam on the backrest, 1" on the sides of the bucket.
Keep the tires at about 18 lbs. Plan your trips on fresh roads.
I use this thing every Michigan "bucket" drivable day. It still can beat the h@ll out of you. Luckily my trips are usually 25 miles or less. On main roads. Only have an 8 gallon tank. So I get forced rest stops on longer jaunts. .