OT: Roof Rack Accessory Install, Trying To Fool Mother Nature...

I am installing a roof rack accessory that Thule calls "Hullavator"
It is, of course, designed to be installed on Thule 1.25" x .75" cross bars.
My setup uses 1.25" crossbars and there is about 5 inches where the racks join the bars and it's wider.
Excess vertical (1.25" vs .75") is not a concern because Thule offers two mounting methods: brackets/clamps for the 3/4" bars and vertical bolts for it's fancy-schamcy alu "Aero" bars... and I'll do that, just with longer bolts through the 1.25" SS box.
Couple pix where I dummied up the install by padding the Hullavator base so it rides on top of the cross bars and does not have to contend with the wide area (highlighted with red tape in the second link):
http://tinyurl.com/lclln93 http://tinyurl.com/n4dvrue
My intent is to take a grinder to the mounting brackets and remove the lips where they contend with the rack joint --- grinding off that 5 inches -- and, just for CYA, drill two additional holes: one near each end of the ground-off area and add two more vertical bolts, hoping they will compensate for the loss in torsional rigidity lost by grinding off that section of lip on each side.
Does anybody see any red flags here mechanically? I
How about corrosion prevention? I've got to put *something* on that bare metal left by the grinding.... and the overall rust-resistance on these things looks pretty dismal.
Maybe that stuff they spray on auto underbodies... or the goop they use for spray-in bed liners?
Pete Cresswell

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.