I decided on progress over beauty and did the outline angle of the chassis
with MIG instead of Tig. I dialed back the Amps and Volts and was ok
in the corners, a couple of small holes in the flat 3mm but I can live
with that.
I finished the complete outline – the outside angle where the panels get glued on and
started fitting the floor.

I use a t section to support the floor panel joint. The t is 10mm lower than the height of the panel, which leaves a 3mm gap between panels, which will be filled with fiberglass matt and epoxy resin for a seemless joint. This will be done  after registration and after I have fitted the tanks.

floor_joint
I also have confirmation on the tank brackets from the laser cutter and the tank senders
are on their way. Needed to order a 115mm hole saw for the tank inspection lids.

I also have decided and ordered all the necessary parts for the electric floor heating.
4 Thermostats for 4 independent circuits – around 10 sqm of heating film to also
cover the slide-out floor areas.