This is how the awning rail meets the upper side rails.

To have more room refitting the awning rail, took the end cap off the side rail.

 
Would have been difficult taking excess sealant off and tooling.

Took an age cleaning the old sealant from the rail, scraped out of the grooves with a screw   -driver, used white spirit to clean the rest.

Fitted the rail without sealant so that the masking tape could be applied, the excess sealant goes on the tape making-

The cleanup easier after tooling. 

Rail removed

Towards the rear.

Marked position for two new fixing holes

Used a bit the same size as the existing holes after drilling a pilot.

Applied Seamseal to the channel the screws will go through.

Then applied 19mm W4 mastic to the centre of the rail.

More Seamseal applied to the edges.

Takes two people to fit the rail to the van, started fixing in the middle and worked to the rear.

After fixing, used this tool that was used on the fridge vents to remove excess sealant.

Sealant oozes from the side of the rail when screwed down.

Then removed the masking tape, leaves a clean edge and nothing on the van side.

A finger dipped into water was used to obtain a smooth finish.

Then turned the screws another quarter turn.

Which left a slightly raised bit of sealant. 

Re-fitted end caps with Sikaflex.

Closer view, use a finger wetted with water to finish off the Seamseal, side rail looks like it has been siliconed, will have to redo that.

Fitted new plastic insert, found that this plastic tool for grouting tiles helped to get it in.

Put the plastic in the bottom groove and using the tool pushed it along, then made sure it was bedded down by pressing.

Plastic insert back in place. Worth replacing if not in good condition.

 
Secured plastic insert under the floor with a stainless steel screw.

 
Ridges under plastic trim, okay if you don't look too closely!