Problems applying Triplewax polish

Hello everyone,
Apologies if there is already something on the forum,  but I wondered if anyone has has this problem. We washed and removed all traces of dirt and algae from the van yesterday.  I went to apply a coat of Triplewax polish to the dull bodywork as per the info on the bottle. When buffing the dry polish, it is leaving a very patchy finish which does not look good!
Does anyone have any advice or tips that might be useful?

Many thanks, 

Liz

Clean a test area with g3 compound or t cut then polish and see the difference.

I have found that some products made for cleaning or polishing cars are only really suitable for the (painted metal) cab areas on the motorhome; they don't always work effectively on the hab conversion parts which have a gel coat. For those, I tend to use products from e.g. Meguiars marine/RV range which are specifically engineered for those finishes.

I used Silky polish on the old van and thought it was quite good for GRP.

You won’t go wrong with this for GRP..it’s brilliant..[You must be registered and logged in to see this link.]

The OP's van is a Sigma so it is Styrofoam and won't be a gel finish will it?

I thought gel coat was what the monocoques had on the body shell.

Paulmold wrote:I thought gel coat was what the monocoques had on the body shell.

i'm pretty sure the roof and rear of my Pollensa are each one-piece GRP mouldings - the side wall panels I guess are styrofoam.

Meguiars marine/RV products seem to work fine on all these.

I swear by Auto-Glym on my Nuevo. It seems to work on metal or glass fibre.

Paulmold..you are correct, the monocoque has a gel coat covering the GRP behind it, if id didn’t have one you would see the fibreglass matting.

Thank you all very much for your replies and helpful suggestions. 
We've definitely used the wrong product on the side of the van. The sides feel like metal ? aluminium, and other parts of the van seem to be made of fibreglass. It would be good to know which kind of paint was used, but it sounds as we would  either have to remove all oxidation from a large area before waxing or try the Auto- Glym. 
The weather in Yorkshire is being typical so we've got time to ponder.
Many thanks, 
Liz

Hello, a little update to everyone who gave me helpful advice on this matter.

We ended up t cutting all the oxidised areas, buffed it off and then used Auto Glym to add a nice shiny surface. It's looking very good and although not absolutely perfect, we're really happy with the result. She's a relatively old van so definitely has had a makeover!
Off to Filey next week, so hope our efforts protect her from the sea air.

Many thanks,
Liz