"First time I've pointed my camera straight down... I nearly lost it a few times!"John,
At nearly 4.6kg without a lens the Horseman L45 is a fat-arsed fish wife of a beast to schlepp about, let alone to point down or put on a boom arm. (I know all too well after just researching what to equip myself with to work with from a motorised wheelchair. The Toyo 45G is even heavier, let alone the Sinar P2 4x5 and 8x10 of younger days.)
I want to suggest that you carry a bit more, althought it's nothing very heavy:
1. A couple of re-usable empty shopping bags to fill with heavy stuff you can muster up on site and place as a counterweight on the leg opposite where the camera if swung,
2. a bungee strap to hang from the apex of the sticks to a heavy anchor (heavy kit bag) on the ground below,
3. go to a camping store and buy long metal tent spikes with elastic loops to hammer into firm ground.
The little carbon fibre Leofoto table top tripod I bought with an accessory weight hook the screws in to the top plate for such a purpose,