Also I think we had this discussion before but what about tankers? Clan Hell's Horses has a lot of tankers and from what I remember tank commanders are usually those who can have bloodnames. if they fight augmented against say an elemental how might such a trial look like? If the elemental gets the choice of the battlefield I would say use a heavily forested area and the vehicle is basically useless
First off, tankers with bloodnames actually isn't that common (based on canon evidence). Among the Hell's Horses tankers and infantry are warriors who failed their first Trial of Position and were relegated to a lesser class of a equipment. So they are kinda seen as second-rung warriors. Insofar as I know, we've never seen a tanker or conventional infantryman command a Hell's Horses cluster, Galaxy or occupy a position of senior leadership such as Khan.
Even in the more recent eras (Dark Age onward), which introduces the TankWarrior. You have sibkos specifically being bred to be tankers from the start. Canon sources tell us that few tankwarriors achieved a rank higher than Star Captain, earn a bloodname, or occupied higher office. It also notes that the discrimination against vehicle warriors is still very present and real, even in the Horses. The whole Tankwarrior concept was deemed to be somewhat lackluster. It seems to continue but has proven to be somewhat disappointing and really hasn't developed much of a distinctive phenotype. I suspect alongside the tankwarriors you still have a majority of the Horses' Tank Corps being warriors who failed their first ToP and were relegated to vehicles.
All that being said, let's shift to what such a Trial might actually look like, and how it might be regulated.
As for The Trials of Bloodright themselves, you just need a vehicle that can be managed by a crew of 1, or modified to do so. We have canon evidence that this can be done. A Ghost Bear Galaxy Commander named Alexandr in FM: Warden Clans as described as being quite impressive and hints that he may even take a captured Athena into a Jorgensson Grand Melee if one-man controls can be rigged. Then by FM: Updates, set years later, he's bloodnamed. It's not conclusive, but this implies he resolved the technical challenges and won. Against an elemental some of the lighter vehicles are better matchups. I can see some Zoryas, Mithras, Asshurs appearing in this role a lot (Other good examples out there, I'm naming vehicles that are common among the Clans and have been around a long time). Possibly with some weapons deactivated to better match the firepower of an elemental.
I can absolutely see an elemental choosing to fight in rough terrain. But there has to be a line somewhere, where an objection would be raised. A completely dense forest (zero paths, zero roads) that allows for zero vehicle movement, gets a red flag, a Neg and a "Select a different battlefield" from the Bloodname House Leader running the show.
Same with an elemental declaring "let's fight on the hull on a space station." Unless that vehicle has the Sealed equipment, that's instant death for the crew while the elemental survives in his spaceworthy battle armor.
A hovercraft warrior getting the venue and saying "on the surface of the ocean" to his elemental opponent. The hovercraft is zipping around the water. The elemental steps off the hovering dropships' ramp and instantly sinks to the ocean floor. Neg.
Some common sense is required here that conforms with the Clan sense of fair play and the concept of actually earning honor and glory via winning a battle. A forest with roads and some fields? Sure. An urban environment with roads and some large empty parking lots? Sure. Paths that a vehicle can use. That makes sense. The elemental can absolutely exploit the environment to try to ambush or outflank the vehicle, but there's still the potential for a good fight.
The person running the Trial, usually the Bloodname House Leader, would be able to veto any silly too exploitive ideas. A venue that gives the warrior choosing it an edge or advantage is fine. But an instant "Gotcha, I win" just by choice of venue is not acceptable.
I suspect to avoid a lot of this nonsense, there are actually a lot of rules and regs surrounding a Trial of Bloodright (remember Clan warfare is very ritualized in its strict form, which a Trial of Bloodright would generally adhere to), that are shared with the participants in writing well beforehand. Not unlike how a professional athlete is expected to know the rules of their chosen sport. Even then the Bloodname House Leader can step in like a referee should anyone cough up something too objectionable.