AVOID unless emergency.
Folks at James Cook Friends Forum were told by Westfalia folks NOT to walk on roof.
The roof is thin fiberglass. The supporting wood frames around skylights and air conditioner don't look like they are supported.by anything--just woodwork between the fiberglass roof and interior ceiling.
Maybe Discus, TNeuer and others who have removed air conditioner will chime in.
Possibilities:
1. Upper Bed Access.
Open main skylight and can access arms-length area by standing on open bed. Can also remove skylight dome for more access to sloped area of roof. Dome can be removed and lowered through skylight opening by tilting unscrewed dome.
If have rear door mounted ladder, would have access to most areas of roof.
For sealing the antenna holes, can reach through removed skylight dome and standing on bed. For oxidation at front end and sides, better to go with scaffolding.
2. Scaffolding.
Scaffolding is great. Gives you room to move sideways and gets you close to roof (most stepladders taper toward top so put you farther from curved fiberglass top.
5' to 6' high works for most folks. Allows you to see and reach most areas.
If don't want to buy, can rent scaffolding. Had rented scaffolding when my solar panels were removed and reinstalled.
Look for "Baker" scaffolding--not as big as construction type scaffolding and useful for interior house stuff as 30" wide.
For front, put scaffolding on each side of front, and planks over the hood supported by the scaffolding.
3. Forklift.
Use a forklift to lift AC off roof (after disconnecting everything). Airstream used forklifts to remove and replace air conditioner.. Others have used pulleys and big trees.
4. Ladders
Stepladders aren't that convenient. If use a straight (not tapered) stepladder like a Giant ladder, might work. Can tie rope at top of ladder and through vehicle windows for security.
Regular ladders could be cushioned and leaned against top corners of roof (not sides of fiberglass roof). May still dent roof.
Autocamp has some nice ladders which can form scaffolding. But I have not been able to locate a source.
http://eat-drink-men-women.blogspot.com/2015/11/new-air-conditioner-for-brunnhilde-part_78.html
5.. Pickup Truck
Maybe a bad idea. Believe some Sprinter owners have gained access to roof by parking a pickup truck with roof rack support frame.next to Westy. Then add plywood on top for a platform.
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That said and before I saw warnings on James Cook Friends forum, I've had folks lean ladders against the top.curved edge of fiberglass top to repair air conditioner and a RV carwash person used ladder to climb and stand on roof to wash heavy.tree sap off (was on the road so no way to self-wash). But better safe than sorry when scaffolding is so much easier and safer.