A friend bought his Laredo from a dealer in Florida. While it was new, it had been on their lot for two years. He had no issues with the rubber roof or caulking at all. I would think two years of Florida sun would be more than equivalent to four years in BC. I wouldn't be too concerned, though I would, as already suggested, get up on the roof and give the caulking a good inspection.
Holding tanks require a dump hose and access to a dump station. As one respondent indicated you can get away with a bucket for a gray tank but I would never want to do so with a black tank. I remember the older Lance 815 had one tank for gray and black which made for some interesting showers when the tank was close to full. I assume they separated the tanks in the 825.
The layout of the Laredo is well thought out for trucks where the rear axle weight is close to being maxed out. With the fridge and the fresh water tank located in the front of the unit, some of that heavy weight is transferred to the front axle. The 825 is pretty much a straight copy of the Laredo with the exception of the extra wardrobe in the sleeping area of the Laredo which is a necessity for couples :-).
I note that the Laredo has a Heiki vent and the Lance doesn't. While several members here have cursed the Heiki vent, I've never had any issues whatsoever with ours and we love the extra light and skyview it affords. The sleeping area can be a dark cave otherwise. And from 2008 on, Northstar sealed them to the roof with Eternabond so there should be no problems with it leaking. Just make sure it has the rubber gasket on the rim to ensure a complete seal when the lid is closed.