Two deep steel I-beams run the length of the trailer, with outriggers and cross-members between them. This is the most common US trailer and fifth-wheel frame.

How BaseRoll™ mounts: BaseRoll™ is designed to bolt between or beside the main rails. On 10 to 12 in beams the unit can tuck within the frame depth; on 8 in beams it sits about 2.5 in below the rail, and on 6 in beams more. Cross-member spacing at the entry door and enclosed underbellies or tanks decide the final bracket.

Class A and Class C motorhomes sit on a truck or motorhome chassis with heavy C-channel rails (Ford, GM, Freightliner, Spartan, Workhorse).

How BaseRoll™ mounts: The rails are deep and strong, and BaseRoll is designed to mount to them. The motorhome builder’s floor, outriggers, tanks and storage bays decide whether there is open space at the entry door, so each coach still needs a look.

Engineered lightweight frames (BAL NXG, Norco Z-frame, huck-bolted Z-channel). Profiles are shallower and shaped differently from a classic I-beam.

How BaseRoll™ mounts: BaseRoll is designed to mount to the main rails with a frame-specific bracket. Where published, a 10.5 in Z-channel lets the unit tuck in; a 7.5 in Z-channel leaves about 3 in below. Most makers do not publish section sizes, so each frame needs more research.

Mercedes-Benz Sprinter vans: a unibody with shallow longitudinal members welded to the floor.

How BaseRoll™ mounts: Mercedes publishes a 4.72 in web. If BaseRoll nests against it, about 5.8 in of the unit hangs below the rail. Listed clearance is about 8 in. Owners report 10 to 12 in of space between floor beams, and the sliding-door step intrudes on the door side. Mercedes forbids drilling the rail flanges and near the B-pillar. Designed to mount; each van needs more research.

Other European unibody vans: VW Crafter / MAN TGE / California, Renault Master / Trafic.

How BaseRoll™ mounts: The VW Crafter longitudinal is published at 4.51 in, similar to the Sprinter, so BaseRoll would hang about 6 in below it. Clearance and door-side layout are not published for most of these vans.

Ram ProMaster and its European twin, the Fiat Ducato / Peugeot Boxer / Citroën Jumper panel van. A front-wheel-drive unibody with no separate frame rails under the body.

Key questions: This is a unibody with no exposed frame rails, so where would a mount attach? Ram lists 7.7 in running clearance on 118/136 in vans (Ram Views & Charts), against a unit about 10.5 in tall, so how much room is really there at the door? On the 118 in van the sliding door opening is 42.3 in, shorter than the unit’s roughly 46 to 48 in length. Aftermarket door-side tanks are sold for 159 in vans (CanadaRV), which suggests more open space on the long wheelbase. Not ruled out; we need real measurements.

Ford Transit and Transit Custom vans: a unibody with frame holes and closed side members, not a separate ladder frame.

Key questions: This is a unibody with closed side members, and Ford does not publish a rail section, so what can a mount attach to? Listed ground clearance is about 6.0 to 6.1 in (iSeeCars), against a unit about 10.5 in tall. An aftermarket 48 in tank fits the door side on 148 in vans without running boards (Agile Offroad / NW Conversions), so that space may be usable. The exhaust hanger is on the door side, and Ford asks for 3.9 to 5.9 in from exhaust parts (Ford body builder guide). Not ruled out; we need real measurements.

European motorhomes built on a van cab (mostly Fiat Ducato, some Ford Transit or Iveco) with a builder or factory ladder frame behind it.

How BaseRoll™ mounts: BaseRoll is designed to mount to the ladder frame behind the cab. Section heights are not published in the brochures we have, and the coach builder’s floor and tanks decide the door-side space.

AL-KO low frames on European motorhomes, and galvanised AL-KO or similar chassis on European caravans. These frames are lowered and shallow by design.

How BaseRoll™ mounts: BaseRoll is designed to bolt to the frame and may hang below it. Because these frames are low and section heights are not published, ground clearance and the door-side layout need checking on each model.

Small trailers and fiberglass campers built on steel tube or channel frames (Casita, Scamp, Aliner, Black Series and others).

How BaseRoll™ mounts: BaseRoll is designed to bolt to the frame and may hang below it. On a 3 in frame the unit sits about 7.5 in below the frame, which uses ground clearance on a small trailer. Fit depends on the door location and clearance.

Welded aluminum frames on a small number of premium and off-road trailers.

How BaseRoll™ mounts: BaseRoll is designed for steel rails first. Aluminum frames need a bracket approach that respects the maker’s rules on drilling and clamping. Section sizes are rarely published.

The maker does not state the frame type for these models in the brochures and pages we read.

How BaseRoll™ mounts: We will not guess. BaseRoll is designed to mount to steel main rails; once the frame is confirmed, the rig moves into the right family.