Just fix one of these or similar to the back and one on the underneath with some suitable screws, IKEA stuff is frankly sometimes a bit naff and need repairing, then move on with your life. Forget about filler...
The conservatory company is wrong (and more than likely they know it only too well) but I too would just do it but build over the drain by the books - that is adopting all of the measures necessary as if you were doing a build over.
That said I would never build a conservatory anyway, they're...
Every council has their own planning policy, it's called the "Local Plan". Within it they provide policy and guidance with regards to how development should be considered within the borough and it's what the planners use to determine whether a planning approval should be approved or not. There...
I bought a Macalister one from B&Q, cheap as chips (£40 on offer) it's utterly crap, needed quite a bit of 'adjustment' before it was anything like flat though does accommodate quite a bit of length (ooer missus). But I can't imagine using a mitre saw on the ground.