I try my best to not put hot glue on the outside of the armour, because it can be difficult to make look pretty. Typically, I use contact cement to do the major holding, then reinforce the seams on the back side with hot glue. If your contact cement is not holding too your liking, consider a few things:
- What brand of contact cement are you using? Some brands simply do not work as well. Whether it's because they're water based, or some other reason, not all brands of contact cement will have a good hold. I prefer to use the Barge brand.
- Make sure you let the contact cement dry before putting the pieces together. If the contact cement is still wet when you put the pieces together it will not hold securely.
- Make sure you have an even, thin, layer of contact cement
As for the state of your armour pieces right now, they are definitely still usable! To cover over those large hot glue seams, try using thin EVA foam, say 2mm and covering over all of the rough seams. This is a technique that Impact Props uses to build his armour. Brad (Impact Props) makes the armour from scratch, without a template, which leaves many rough seams from making adjustments. He then goes over all of the armour with thinner foam to add details, but also hide the gnarly seams.
You could also consider smoothing the hot glue seam with the nozzle of the not glue gun, although I don't know how well that will work. You're best best is covering the seam with thin foam.
7 hours for two pieces is not a-typical. Especially if you're new to foam crafting. Don't be discouraged that it is taking so much time. I spent roughly 60 hours doing the foam work for my most recent suit, which also happens to be a mkVII. I ended up making my thigh pieces twice actually, because I originally made them too small haha. It's all part of crafting. Best of luck continuing on your build! We're always happy to answer any further questions you man have!
Edit: Also, if you want to see my general foam crafting process, check out my tutorial on YT that
MrBones linked above