Chariot sells a cross country ski kit for their bicycle trailers. They're spendy - around $200. I decided to make my own. The kit you buy consists of two skis, their mounts and a harness to pull the rig. I decided to pretty much copy the commercially available unit.
A pair of skis
2' pvc pipe
foam floor padding thingy
1' wide nylon strap
nylon strap buckles
I don't exactly remember what all I used.
Skis: I found the skis I used at REI on closeout, clearance,we've got a bunch of these and NEED to get rid of them for a low, low price of $17. They are simply a pair of child's cross country skis. I think they are 110cm long. Had I not stumbled on that incredible deal, I'd have visited thrift stores, watched garbage piles and/or made my own from pvc maybe?
2' pvc pipe: Environmentalists relax, yes I know pvc is bad stuff. I found a piece of it in the rafters of my garage. It must have been leftover from a project performed by the previous owner.
electrical conduit: I bought mine at Home Depot. No real mystery here.
foam floor padding thingy: This was one of those puzzle piece square foam play mat things. I used a scrap I'd kept after cutting it to fit the floor in my basement so my little one would have something softer than concrete on which to play. Approximately 1/2 of a 2' x 2' square, so 1' x 2' was perfect.
old seatbelt: When I was in college I worked in a shop maintaining the college's fleet of vehicles. At some point we had a big 15 passenger van with only the front two seats. Strangely whoever removed the seats left the seat belts. We removed the seat belts and the guy in charge threw them in the trash. At the time, I didn't know what I'd use them for, but I knew I'd think of something eventually. I saved them. Now 10 years later, I've finally thought of something to use one of them.
nylon strap: More stuff I had on hand. Most of it came from an old mounts on the back of your car bike rack. I think one piece was something I picked up on the street and the final two were from a backpack maybe?
strap buckles: Surprisingly I had these on hand too. Maybe from that backpack or ???
Step 1: The Ski Plan
First thing to figure out was how to attach the skis to the trailer. The commercially available kit has two triangle shaped things attached to the skis and then an axle that plugs in where the wheels' axles are. I thought about doing similar, except the axles have a nice push button quick release feature. I didn't have any extra axles lying around. I decided what I'd do was build a 'socket' into which the existing wheel would fit. I liked this idea as it made the skis more compact for transport and storage. It also means that I can roll the trailer across parking lots, roads, sidewalks or other snow free spots. Simply remove the skis from the wheels, roll across the road, pop the skis back on and away we go!