I've literally just posted a thread on this yesterday evening. I'm a LR RWD but efficiency wise you'll exceed 4 miles per kWh on the motorway this time of year if my experience is anything to go by.

https://www.speakev.com/threads/what-do-i-have-to-do.186300

 

We still have the 64kWh Soul, but I now have a model 3 LR AWD from 2021. Extreme bad weather range was around 230 miles with 19” wheels. I would expect better with 18” wheels. Obviously the new RWD has less range, but has an LFP battery so can be charged to 100% regularly, so will in reality do a similar range to the AWD on 80%.

The model 3 is very efficient, especially the RWD version. Much more so than the Soul with its brick like aerodynamics. Though it is pretty good, providing you keep the speed down.

 

I’ve been unable to tell the difference in consumption between my iD4 with and without the roofbox. In fact I’m convinced consumption is better with the roofbox! Maybe I just drive slower…

 

Be careful in your roof box choice maybe. We have a Thule Ranger 90 which is a "soft" roofbox and were getting 3.6mpkwh in October at @12 deg C . We'd normally get 4.6mpkwh

 

Yeah I went with a rigid aerodynamic box, Modula Wego 450L, Thule knock off copy I suppose. Pricey but it will take larger items like body boards, flat fold chairs etc and has all the gas struts, quick attach/release and dual opening etc

Honestly If I had a second EV with 150 real world summertime motorway range instead of the Leaf I wouldn't have bothered and just taken 2 cars instead. I'll only use the box maybe twice a year at most for perhaps 2 weeks max. It's a crazy amount to pay when you include the roofbars cost.

In your case the extra cost of the efficiency loss isn't all that much in the grand scheme I suppose.

 

I went for Thuel Motion XT Sport. It is the shiny black long thin one, good capacity and can fit a bike alongside it. Very spendy indeed for a bit of vacuum-formed plastic but it looks really good on my black iD4 and you really do get a lot of stuff in there, I’ve bought 3x mid-size hold-alls and 2x large ones from Amazon that fit perfectly.

As I say don’t sweat the range “reduction”. I went camping last week to the same place I went a year ago. Last year no roof rack, box, or bike, and I had to hypermile to get home on 4%. This year with roof rack, roof box, and bike I got home on 12%. Obviously there are a gazillion inconsistencies that are impossible to account for but I’m confident that the roofbox doesn’t harm range as much as you might imagine.