A fixture is provided for supporting load from weapons recoil, being mountable on a flat bed of a road vehicle disposed on ground. The flat bed can receive a weapons mount. The vehicle has longitudinal, lateral and vertical orientation directions. The fixture includes a horizontal deck, a slide assembly, a dampener housing, port and starboard lateral beams, together with first, second and third posts. The horizontal deck receives the weapons mount. The slide assembly supports the deck. The dampener housing receives the slide assembly. The port and starboard lateral beams extend laterally from the dampener housing. The first and second posts extend vertically downward from their corresponding beams to engage the ground. The third post extends vertically downward from the housing to engage the ground. Brackets on the slide assembly extend longitudinally from the platform for enabling the vehicle to drive away from the fixture. The posts are retractable for stowage and extendible for raising the flat bed above the ground.