If possible, try and get hold of a replacement circuit board to "try out". (maybe if you know another camper friend who has same heater, offer a "koha" and borrow theirs ??) The PCB is very easy to replace (about 2 minute job if heater is readily accessible, undo two screws on plastic triangular cover were wires enter unit, gently undo the two plastic plug connectors and gently lift PCB up and out. Installation is same, ensuring PCB pushes into socket at bottom of heater (this is where the wires to the igniter goes) ) and if heater works ok, fault is more than likely with PCB.
These are not cheap ($399 or so - total rip off). There is one on Trademe at present for this price. We had similar problem, i.e. turn on, click and red light would come on after about 8 seconds. Sometimes it would light after several attempts, but problem got worse. The red LED indicates gas burner has not lit (or overheat temperature has been reached).
When I got frustrated and did not wait for several minutes before re-light attempt, there were frequent gas explosions, best to avoid these.
To see if ignitor is working you could try listening very close to outlet grill (on outside of van) while somebody operates heater switch). You may be able to hear clicking as this is the igniter working, which may indicate no gas or overheat sensor fault. Keep ear to one side in case it goes bang.
Another fault may be leaking tank and water drowning burner (but with this problem you may see water dribbling out of drain on exterior vent. The 30 seconds before hearing "click" seems a long while, ours clicks 2-3 seconds after turning on.
Could be other faults apart from PCB (no gas supply, overheat sensor gone bung etc - there is a fuse on the PCB but I don't know what this protects - whole PCB or parts of it).
After parting with $390 for another PCB, I (as a long shot) replaced two small relays on PCB (at cost of about $2.50 each !!) and PCB seems ok, although I wouldn't guarantee long term, but it will do as a spare.
However, as mentioned, do a search for truma on this forum, and Google "Truma Ultrastore", you can find a spare parts diagram which shows PCB and all other bits.
Lets us know how you get on.