Well, Portable Bunkers are not generally allowed at most games. Generallly, anything you are carrying is part of your gear and if hit, is a kill. So it gets complicated and easy to start controversey if you were REALLY Stationary or not with they started shooting at you. So check with the field and producer first. The guy at D Day had a in with the staff and I will bet $100 if I showed up with one just like it and wanted to play Allied side, it would not be allowed.
A thing called a PUG or Walking Tank is not allowed at many games such as D Day as they are considered "portable bunkers". I run a walking tank and share designs and plans for them. Much more complicated to build than what you are talking about.
But it is considered armor or 'light' armor. Impervious to paintballs. Takes a satchel charge, RPG or tank Round, or attack helicopter to kill it. Mine is backpack based so it is VERY portable. Can break the 5 mph speed limit for armor. It is 65 pounds battle ready including an auto loading cannon and a 25 pound SCUBA air tank. Without the cannon and extra air supply, it would be 30-35 pounds with just a marker.
Also made a pair out of 1" thinwall PVC pipe. Have a BETTER design now than this to share with anyone interested. Again backpack based and considered armor. You don't have to have a cannon either. It will drop 30 of the 70 pounds of hardware if you omit the cannon and just use a marker. Very playable at 40 pounds.
Below is a walking tank concept I have been pondering for a few years now. It is a flawed design but is more like a portable bunker than a Mech Warrior.
Imagine NO FRAME and NO WHEELS. Just a SLED that looks like a tank. The tank tracks are the 'runners' of the sled. The trick is to build it light enough for two guys to have FUN dragging it around the field. That has been the problem with the vast majority of walking tanks. Weight.
I solved the problem using 1/4" - 6mm polycarbonate twin wall. A 4-8 sheet is about 7 pounds. 1/4" 4x8 plywood is about 20 pounds by comparison. Very LIGHT, very STRONG and very Expensive at $80 a sheet but you don't use a lot.
I mention that because your original idea would find this extremely light and portable. 4 two foot wide sections, 4 foot tall would haul on your back and weigh max of 8 pounds. Heck of a porta-bunker.