What a c**p website for information :

I had a good look and there is no specifications on any of there products?.
The only information I can give you with the lack of specs are as follows.
If your original relay had a 15amp fuse then it should be capable of charging upto a 150Ah battery, yours is 115Ah so within the limits of the relay.
The only advice I can give you is the next time you run your van, check to see if any of the cables are getting hot (some should get warm) but not so hot it feels like the outer sleeve is soft, if the later is the case, then you still have a problem, I would suggest you try another battery and then check your cables again.
If you continue to get problems after trying another battery, then get your alternator checked by a pro.
If next time your fuse blows, don't just replace it, assume something else is wrong to cause the fuse to blow and run the check list above.