So I watched, I think, all of warehouse 13 a little while ago. Like more than a year but I can’t remember how long ago. Pretty sure I got to the end. Been watching eureka lately and woa. Episode with someone from warehouse13. Thing is there may have been a crossover episode in warehouse13 but since I did not know eureka I may not have recognized it.
As others have mentioned theres two bespoke crossover eps (i think theres two in eureka too, but maybe just the one).
They also make a lot of throw away references to the other series, like the computer guy saying his “new life” (in Eureka) was too hectic