For my RadWagon4 I found this lock in my local bike shop - Texlock Eyelet. It's a mix of textile and cable lock that's supposedly cut resistant due to the mix of materials (as bolt cutters aren't really sharp and angle grinders get tangled up in the textile shell). Due to its ability to loop one end through the other, you get a lot of reach with it to wrap it around stationary items. It wraps nicely around the caboose so I can keep it on the bike at all times without having to take off the loop or having to put it in any bag.

As a bonus, it's also made in the city I live in - Leipzig, Germany. So it's really a local product, but from what I understand they also ship it internationally.

I have the large version with the mini U lock.

Apart from that, I always look the front wheel to the frame with a large Abus U lock with their security grade 15 (maximum) and also have an Abus 110cm folding lock. I don't use as much anymore since I got the Texlock as it's much more difficult with it to reach around stuff, but I always use it at home in our yard to attach the back wheel to my Texlock overnight. Even though we have a large gate, there's already a few bikes that were stolen and they also once took my RW seatpost+saddle, which sat me back 120 EUR or so to get a replacement. Now I secured the seatpost with the Pinheadlocks system.

I actually ended having my bike shop build the wheel for me. I found a Novatec fat bike hub that they ordered and using a sturdy 24" v shaped rim and a Schwalbe Marathon Winter wheel, they built the wheel for me and it fit beautifully (I was worried the v shaped rim would make everything too big, but it fit with no modifications to the fender.
All I did was switch the break disc from the existing wheel to the winter wheel.

It set me back 300 EUR in total, but I felt much better doing the daily day care run with two kids. As it was still around freezing in the morning, I still have it on, but I'll change back as soon as I get a chance.

Of course, what you lose is the suspension added by the original fat bike wheel. So the ride is maybe a bit bumpier.

Calson,
I think you missed that the RW4 tires are 22"x3" that are a custom size from RP that's nowhere else available yet. So unless some other manufacturer did by now pick up on this, they are only available from RP. So the complaint was a legit one. That said, at least in the European shop the tubes and tires have been available for some time now and can be readily purchased last time  checked.

With the fat tires, the correct setting is the default of 24". So I'd put it back the way it was for correct speed / odometer readings.
Enjoy your wagon!

Hi Antti,
nice idea and findings!

How do you plan on doing this for the back wheel or would you keep the current tire on that?

For the front wheel, I did come across a slightly less costly front hub (Novatech Fatbike) which I've seen for around 50 EUR right now in Germany.

On first look, the 24" inch rims aren't as easy to come by either. I'm looking for one that would fit the Schwalbe Marathon Winter wheels (47-507). Did you already come across a brand?

I've also never installed spokes myself on a rim and have to read up on what length I'd need, which I guess depends on the installation I'd want to do.

So if you'd like to share any more details, I'd be happy to hear more on your plans and progress on this.