Camper trailer traveling cover larger replacement

Local auto upholstery shop would be a good start i'd guess.

Go careful on loads on the tent.
Unless travelling gentle bitumen mostly, things may wear the tent badly with movement, corrugations / undulations etc.

Or at least use ratchet straps across the load (before covering) to keep relatively stable.
Maybe a throw over canvas ground sheet (doubled over ?) on top of the tent between that and the chairs etc would be a good idea too.

I did exactly this to my old soft floor camper. I added 200mm to the height - the upholsterer reused the top and zipper, he just added a 200mm strip around the edge to give the extra height. Can’t remember who did it (someone in Adelaide near Para Hills) and cost about $200.

I kept all the sleeping gear, chairs and tables in there. We used it for 4years off-road (rough-ish dirt roads, not constant corrugations though) with no issues at all.

if your in victoria try southern cross canvas in bayswater they are excellent