I always use sash window cord from the local hardware store, find it's thicker than some. It pulls the seal wide enough open to come over the lip I have used chain saw pull cord once when i was stuck but it pulled out between the seal and the lip before the seal was pulled over. I put it down to it being too thin
Mine were a bit of a pig 3/4 windows that means they have 2 square corners, but warm seals good strong string (i used 1.5mm cable stripped out of some twin and earth) Shielsy's method of inserting the cable into the seals is excellent too, it involves using a silicone nozzle but really does make it easy. someone pushing the window at the point you are pulling the string / cable and a bit of patience and in they go. Good luck
Ok all windows are in except the windscreen. New seal on order as incorrect one supplied (no lip) Dont know if it will help others but here are some pictures of how i managed to get them in. 1. Park near a wall 2. Find s nice long bar and 2 pieces of wood 3. Put a nice big bit of wood on the window the bar at an angle and a bit of wood between the bar end and wall. 4. Take a hammer and use all the frustration of 4 days of window fitting to apply pressure to the window by hammering down on the pole (wall side) 5. pull the now seated windows string to get lip over and seat the window properly It was really amazing how much the window can take and eventually moved when the seal lip got put over, the bar became loose and fell to the floor as all pressure was let off.
I once had to stand on the windscreen with both feet, hands on the wall. Then I watched a fitter do it. Make sure it's perfectly centred, then top and bottom together with extra loop. Since I've been doing this they fall in.
I fitted my glass the same way as you . i got to a point were i didn't care if the glass broke, i brayed the piece of timber until the van was leaning away from the wall, it worked in the end. For the windscreen if you haven't already done it , use two ratchet straps with the doors wide open , mine popped in a treat , it was by far the easyest one to fit ,good look....................
Here,s another good tip !! Once you've fitted your new screen ,try not to let the wiper arm spring back against the screen without a wiper blade . this could crack your new screen before the van has left your garage . this could be very upsetting after all your hard work , and leave you wondering if it is all worth it !!
Car window cleaner (Fast Glass or similar) is a really good lubricant that doesn't cause corrosion (like fairy) and doesn't perish the rubber (like oil). It also wipes off / evaporates quickly so you can't put too much on and make a mess. Great for fitting Westy louvre glass too.