Mark,
Both Carafax and Sikaflex are widely used in the automotive and leisure industry to seal panels etc, these products is known as one part sealants and are neutral curing. Where Clive went wrong probably was to use the wrong type of sealant.
Silicone is a bit of misrepresentation, as the product is a sealant made up of lots of different chemicals and several key components - Silica sand, Water and an accelerant for curing.
Clive probably used a " High modulus" type which cures very quickly because it has an active ingredient that makes the sealant go hard when it is exposed to the air because it hardens it then doesn't have any give, any joint will then fail and the result will be a leak.
Where as "Low modulus" Silicone forms a skin on the top to give weather proofing and appearance of rigidity, yet under the surface it won't have cured so as to give flexibility. - It use is the UPVC industry and in cosmetic areas of automotive appearance.
Finally "Neutral cure" doesn't have any - chemical accelerant in the tube and therefore fails to set hard it naturally cures over time - 25 years plus. It's main advantage is that because the accelerant chemicals are not present it can be used in more situations with sensitive materials - Aluminium for one is known to react to High Mod and some Low mod sealant - tell-tale signs are a purple tarnish or residue. Equally on PVC it won't react with discoloration.
Essentially you get what you pay for to a certain extent it's is best to seek the advice of one or two local caravan repair centres having said that Carafax, Sika and Wurth also known as (Sebesto) all make Suitable products for your situation.
Good Luck
Monkeys husband
Scott,
If you're doing this then here is the trade's way of doing this repair.
1. Remove the rail carefully, making sure that you don't stress the rail - good tool to use is a decorators putty knife.
2. Measure the screws for length and gauge.
3. clean off all traces of the old sealant giving it a wipe finally with white sprit
4. using a matches box - wrapped in 1000 grit wet & Dry gently rub the surface only where the new sealant is to be applied.
5. Repeat points 3-5 for the rail
6. Gun sealant or apply roll to van - then with helper mount your clean new frame back on the van.
In answer to your questions
Yes you can use mastic roll but it tends to be a bit thick in most cases - however if your van is of an old design then it could accommodate the material with a recess. (The packs I would guess O'l sell are 5 metres)
As for your choice well I like Sika products and so my choice would be Sikaflex although the Seamseal CV does look good for the job, the one to avoid in my humble opinion but also that of my colleagues is Soudal - (s**t in a tube) I was once told by a man of 30 plus experience in this business.
When you refit try to use A"2 grade stainless steel screws applied by hand or your screw(Muller) the head with a cordless driver.
Give the guys at O'Leary's a ring - very helpfully and knowledgeable and one of the few companies still building custom motorhomes !
Kindest regards
Monkeys Husband
Facebook
Twitter