I've always had this issue, but I'm trying to bike a lot more this summer than last year as the wife got her own REI ebike. I cannot get the seat to stay at the height I want.
It has always slipped in. Basically, if I have any sort of sideways tension on the set, like, you know, pedaling, then the seat slips sideways and down.
I only weigh 215 lbs so its not like I'm overweight for the bike.
I have both of the seat clamps as tight as I can. I tighten them to the point where I can't actually close the clamp, then let off a half turn, and then close the clamp. The bike seat still slips down once I start riding.
Any advice or ideas?

If you want a scooter, you should just go buy a scooter. There are several great electric scooters out there.

Thule's website says 40lb limit. 16kg ~ 35 lbs.
https://www.thule.com/en-us/child-bike-seats/rear-mounted-child-bike-seats/thule-yepp-maxi-_-12020214
My experience is that my 21 month old would not hold on very well in the Caboose but she loves being in the seat. But I'm very confident with my 3.5 year old back there. He'll never ever let go of the caboose supports. Its up to you I guess. If you think they are comfortable not being the seat, then go for it. I think the caboose is awesome and a great way to keep them safe in case of a tipover.

The large basket from Rad also doesn't mount to the head stay. You have to buy the flat rack and then mount the large basket to that.
I bought the small basket for the front of my rad wagon and absolutely love it. We have a caboose and one yepp seat in the back. But I also have put a milk crate back there and had it attached to bike via bungie cords and that worked great. Got several bottles of milk and beer in there and felt very secure.

I used the cover on Friday when the first rains of our "Bomb Cyclone" hit. The cover completely covered the bike. On the bike right now, I have the front rack and the caboose (but no Yepp Seat yet). The cover completely covers the entirety of the bike and kept it dry. I did notice that there was some seepage through the cover onto the bike seat. It was not a lot - maybe like 2-3 ounces. I think in the future I'll keep a plastic bag at the office and toss it over the seat if I think its going to rain a lot.
Because we did get a heck of a lot of rain on Friday. And then on the ride home, a WHOLE HECK OF A LOT MORE rain. It was raining so hard I couldn't do anything but laugh at it. Thank god it was relatively warm out.

There are two clips to run through the bike tires so it won't blow off and some holes so you could lock a true bike lock through the unit. My parking area is relatively secure so I usually just lock out the battery and don't always put a lock on the bike.

As for a $22 investment, seems like a good one so far. We'll see how it holds up to 2-3 days a week for an entire winter.

I read several threads on here and other places and I just ordered this one https://amzn.to/3GqoX0U

It should arrive tonight. I'm going to be using it only at work during the rainy season (Tacoma, WA). So it doesn't have to go through the harsh winters elsewhere.

I'll let you know if it fits with the front basket and Yepp Maxxi on the bike.

I got it because I wanted something relatively cheap because its not going through the harshest weather but it does rain. If its too flimsy, well, it wasn't that much money.

Well, today was the first rainy commute. Wasn't a hard rain, but it had rained all night. Lots more standing water in the bike lanes along the busy 6 lane street. So, pretty wet feet. The bike rain jacket I have doesn't breath very well, but it was cold this morning so that was fine. Ski mask was a great late addition keeping the face dry and warm. And doubled up on the gloves. Excellent choice there.

So, cold wet feet, and very wet socks. Hoping they'll dry by the time I head home.

Any specific recommendation for water proof shoes that will work on normal flat platform pedals?

What are you all wearing on your commutes?
We've hit the rainy season here in the PNW and its discouraging me from getting on the bike. I have a 10-12 mile commute (one way) mainly on roads competing with 18-wheelers and other non bike friendly individuals.
On my old analog bike, I was decked out in rain gear and clip on shoes with toe covers or full shoe covers.
But with my Radwagon, I am unsure what to wear on my feet. I have been wearing some running shoes, but that is not going to stay dry. Also, my normal rain gear is designed to breath as I'm working hard, but obviously I'm working less hard on the new bike.  So, sometimes I'm cold, and sometimes excessively warm. Part of getting the bike was to reduce the amount of changing clothes I had to do at work, but that does not appear to be working out.
So, what are you wearing? Feet wise? Clothing wise?
What have you tried that was a complete disaster?

Do you think you could get two Bobike seats on the wagon rack?