im a windsheild tech, i work for glass america here in CT
sometimes the safelite guys arent that great... dunno tho
its possible that the gasket itself is cold, if you have another car, stick it on the dash with the defrost blasting at it (when i do one like this in the very cold, i usually get to that point and sit in my van with the defrost blasting at it, and that helps a boatload)
different gaskets can make it harder or easier depending on the situation
these types of windows are easier if you dont rope them in but place the gasket in place then settle the window in the bottom gap, then using a fiber stick, follow around the outside, afterwards putting in the spacer, make sure he is evenly putting the window in left to right, as sometimes it can be mis spaced and putting too much pressure in one spot
it usually should only take a little bit of silicone lube spray to get it in there
when the guy comes next, go out there and meet him, tell him to get his suction cups out, which he should have, and help him do a 'dry set'
which means you put the window in without using whatever holds it in place, windsheild glue or in this case the gasket
line the window up with the pinch weld, it should look like it should fit real nice, if not, theres an obvious problem
also, sometimes glass shops order glass and they order the part number for the vans that are the same years as our trucks and the same rubber set style, if you put them next to each other they would look virtually identical, but they arent, the van corners are much wider, this has happened before
also sometimes the aftermarket glass is not 'perfect' size, this can be a big problem since you are dealing with a rubber gasket and not just windsheild urethane
and when he gets there next time, i assume you are getting 'new' glass from them, ask to see the glass, if you are having safelite do your work, they will give you the glass that they make, its ****, its the worst glass made, it pitts within a year and it will need to be replaced again, i have never head as many complaints as i have from them, mostly from the glass they make, check the glass, the top companys use 3 letter abbreviations, safelite uses SGC 'safelite glass company', thats the crap you dont want, use PPG or LOF, both make good glass that is often used as OEM glass, but safelite wont let you use anything else, you are better off going to the junkyard and getting a peice of original, they might let you do an R&R 'remove and reinstall' meaning they use your glass and you only get charged labor, this would be the best way to go, i hate to see you end up with their crappy glass
good luck, hope this helps, let me know if you need to know anything else