Greetings,
First question: Where was it manufactured? If made in US, no problem importing back into US. If made in Canada, a few more issues, but not a big problem. Is it a drivable unit or is it towable unit? Different regulations apply.
USA made, and you are a US citizen returning with your newly purchased towable RV, declare it at the primary booth that you show up at. How did you pay for it? If cash of $10,000+ was carried across the border, you had better stopped on US side and reported that $10,000 cash prior to crossing the border or you will be in for a nightmare of a problem. It takes all of five minutes to stop and report the money and you will have no hassles getting back, provided you ask for a copy of the paperwork to show when you cross back over. Once method of payment (over $10,000 cash) has been determined you will be told to have a nice day and enjoy your new camper.
If the camper was made in Canada, all you will need is a sticker or letter from the manufacturer stating that the RV complies with the US DOT safety standards. The money question and issues will be the same as stated above.
There is NO 72 hour waiting period on RVs being imported into the US. If it is a drivable RV other regulations apply (US EPA sticker or letter from manufacture required) so if you have other questions, send me a PM and I will give you my home e-mail address. Good luck and enjoy your new RV.
Lakeside