Sorry I took so long to get back. As far as the hole foam thing for the mercs I don't know why they don't allow it but from what I've seen they normally have good reasons for blocking stuff. Pvc armor I like alot. I just bought a six inch diameter piece of pipe it only came in ten foot sections...
You might try filling the arrow head with resin. I filled my ear caps for my mandalorian helmet. Just remember to be careful my ear caps got really hot when I filled them.
I built mine out of pvc pipe I cut and heated to shape it to me. I built helmet from the wizard of flight template. The mercs don't allow. Foam builds for official builds I've seen one in the unofficial section. I think I'm not sure but I think you can use foam on the back of sentra or trash can...
Good luck on your build. You can check out the Mandalorian Mercs for some advice and help. I'm working on a mandalorian suit too. What do you plan to build the armor out of?
To get something in pepakura to unfold it someone must make a 3D model of the object in a modeling program and then take it to pepakura designer buy a product key or code I don't remember what it is called so that person can save the file and have access to all the tools and start unfolding...
Update
Got the parts stuck together after I get the harness attached I'm going to do a little more shaping to get it to fit better
Picked up a few nylon tool belts and made this I plan on attaching this to the back of the armor