It really isn't that hard. You don't need a broker and you can download and fill out the forms in advance. Call the actual port of entry you plan to go through and talk to an officer there. Explain the situation and see what they have to say. They will tell you what forms and information you will need when you are doing it yourself.
I bought a custom made sailboat (no title, no manufacturer ID) with trailer in Victoria, BC. Bill of sale was important document along with boat number (vin number equivalent). Canadian customs wasn't an issue. US customs, you go inside and give them all the paper work. Items of Canadian origin are covered under NAFTA so no customs fees (tariff) on most items. You can lookup the harmonized tariff schedule code for slide-in campers showing "Free" or 0% (8708.99.81-30). If you are importing something manufactured in Canada a letter of origin makes things easier (MCO).
Customs paper work, bill of sale and Manufacturer ID # will then get you the title. Trailer was more of an issue due to needing temporary insurance and changing registration in BC, then conformance to US standards and inspection but you won't have to deal with it.
Don't go through Blaine (Peace arch, (360) 332-5771 import specialist branch), unless you and everyone in the car has a Nexus card. Head east a little and go through the Pacific Highway (PH 15 to SR 543; (360) 332-7237) or Lynden crossing (PH 13 to SR 539; (360) 354-2183). Less waiting. Your can see border crossing wait times on the net to allow you to pick a good day of the week and time without having to sit in line too long.
If you are really concerned, do a dry run and spend a nice overnight in Vancouver and then come back through US customs, stop in and talk directly to the officers you will be dealing with and make sure you have all the forms you will need.