If the 250 uses mounting hardware as shown in the E-Trailer photo, you should be able to mount directly to the factory cross bars.

I would not use Thule square bars as you would need expensive adapter towers and fit kits to adapt to the car (unless Thule told you something else). The Thule fit kit system clamps to the factory cross bars when they are in the F to R stored position. It's a crappy adaptation in my opinion and shouldn't be needed for what you are doing, especially as you state you have the original 250 hardware.

The attached photo shows that the mounting hardware should work on a cross bar that is under 4 inches wide, the Subaru cross bars are 2-1/4 or so, so this should mount directly.

The reason I don't like the current Thule fit kit for the OB is it installs with a front to rear spread of only 24 inches. The factory cross bars give you 30 inches, so a bit more F to R support, or at least less flex in the box.

 

Thanks we are looking at it now - it came with 2 long rails and 2 short rails. Thule said to attach the square original rails to the rails of the outback, But your input on the spread makes a good point. I will be pressure washing it Saturday and looking at installing Sunday, but not taking off until Friday. Just want to make sure all fits good. Sure maybe I could find the pieces for mounting at Lowes or Depot...?

 

As a long time Thule user with square bars as well as roof boxes and bike trays, I've been thru fit issues on 5 Subaru's now.

Not sure how Thule intended you to mount it's square bars to the factory roof rails. They sell a tower and fit kit, but finding the exact model info is a PITA on the Thule fit guide website. The only version I'm aware of is a tower unit that clamps to the factory bars in their stored positions. Note I am assuming you have the same factory rail and cross bar system common to OB's in the non Touring line, for a few years now, where the factory cross bar stores on the F/R rails.

I modified a set of square bars to install on the factory tie down points, then discovered my Thule Ascent roof box sat to far to the rear to allow the hatch to open fully. I then plunked down cash for the (superior) Yakima system.

There's a whole thread here: http://www.subaruoutback.org/forums....org/forums/138-gen-5-2015-present/174042-2015-outback-yakima-crossbars-18.html

With a set of brackets as seen in the post photo above, from E-Trailer, you could easily just mount the 250 box to the factory bars

https://www.etrailer.com/question-115945.html

 

Finally figured out what the clamps were on the sqaure bars - clamping the rack onto the old drip channels that cars used to have. Felt like a fool trying to clamp them onto the roof rack like the Thule rep told me to. Guess that was Lightingguy was talking about with the adapters and such. Going to use the stock rack system with ubolts and metal pieces to hold the carrier on.
Now still thinking about painting it. Not sure what type of paint to use. Think the Thule 250 is more fiberglass than plastic. Or just real thick plastic.

 

Its plastic, or a version of.

My wife, who paints professionally (movies, TV) frowned when I asked. She said maybe a light sand to roughen the surface, then enamel rattle can (Krylon).

Maybe and unless somebody here more knowledgeable can answer, head to an auto parts store for advice.

A Google of "how to paint a Thule roof box" led to this stuff.

https://plastidip.com/our-products/plasti-dip/

 

Roof cargo box is probably ABS plastic. I patched one a few years ago with white ABS plastic and painted it with a aerosal epoxy paint.

 

Thule 250 Cargo Carrier

Nothing ever works out!
Using the subaru cross bars the thule carrier is too long - can not open the back hatch much

Then used the 450 crossovers on the thule bars that came with the carrier.
The dip in the carrier is too wide - it does not sit on the cross bars correctly.

So, enter husband with his engineering thoughts, cut a piece of 3/4 plywood - bolted to the thule square bars.
Drilled the holes no problem.
Painting the wood now - let it dry overnight.

Then will cut a piece of 3/4 plywood to go in the dip area of the carrier on the inside.

Then bolt the carrier to the plywood that is bolted to the square bars.

The thule bars - The bars barely fit - they are only about 46.6 inches, but is only a 1/4 inch from being exposed so just no end cap on them.

Plus, coming back from the hardware store I had a thought on what to paint it (but will have to wait until I get back from this trip coming up as I want to spend time painting without being rushed.) Decided on the Navy digital Camo scheme.

You may be asking - why not just a Sears XCargo top - had aone before and sold it, never thought I would need it. Silly me.
Thought about getting another one this morning when we were trying to figure out how to make this work.
But I like the old box - It is study as heck. Stuff is not as good quality as it once was.

And the hieight gained using the bars and the wood, the back hatch will open.

Will post the outcome later....This feels like the cargo carrier soap opera.