Here's my stab at a 3-Gun cart. The basis is a 4 wheel Upright Golf Caddy. It's collapsible and fits in the trunk of my car easily. It has a built in brake to keep it from moving on uneven ground. I don't have enough posts yet to include a link. However; you can search the net for "upright caddy golf 4 wheel push cart" and review the offering.
I added two decks to the base of the unit and a typical ATV double gun holder to the upright. One deck supports and positions the butt of each gunstock while holding the guns vertical when nested in the ATV holders. The second deck holds my gun bag in front.
I use the Safariland ELS and QLS so I placed receivers at various locations to hold my gear. The locking system holds my pistol, pistol mags, rifle mags, and shotgun mags in open space for easy transition. So far it has performed reasonably well.
I will supply close up's upon request.
Caddy Closed
Caddy Open
Loaded angle 1
Loaded angle 2
Brian