Welcome Kat, from another BC'er. How many in your family/what ages? I have a 2004 Trillium
Outback that I picked up 2nd hand 4 years ago. It took me almost 5 years looking for an all fiberglass trailer before I found one that was in good condition/affordable. Also looked at a couple of Bolers. One was in bad shape and needed a lot of work with skills I don't have, didn't want to learn. The other one was totally restored but the fellow wanted too much money for it. Very happy with my Trillium as it arrived in good condition with lots of well thought out upgrades by the previous owner.
Yes, I understand what you are saying about the reviews of the Trillium, but my guess is that they mostly have to do with dealing with the manufacturer in Calgary. Promises seem to come and go along with dates for delivery, and communications sound difficult. Other than that, if you were to order a new one, every thing I've read or heard about these trailers has been pretty positive. Now if you are looking at a 40 year-old anything there are bound to be issues of some sort. Whether or not the seller has dealt with them or not, and properly would be a deciding factor for me. And how much time and money you want to put into a "Project" trailer. Both can add up pretty quickly.
I took mine to Inuvik on a 3 month road trip and the only problem I had in 10,000 km was the fact that the mudflaps on my 4 x 4 truck were not good enough to protect the front of the trailer which sits on an 8 inch drop hitch. So I think it's a pretty solid unit after many miles of gravel roads.
Maybe attend the F.G. trailer rally
at Fort Langley to have a look at the variety and ages of trailers if you're in that vicinity.
Ask any questions you like and I'll try and answer. There are lots of people on this site with tons of experience with Trilliums, etc. Have a look at the buyers checklist in the documents section.
Good luck in your search.