what will the gravel do for you? unless you put a weed barrier under the gravel the vegetation will grow through it. i use a weed wacker to trim around the tunnels.
my tunnels (4) run east/west. i did this to maximize sunlight and minimize shadowing. i'm sure other orientations would work too. it gets very windy here too and rather than orient the tunnel based on wind direction i used concrete and anchors to hold down the tunnels.

Easy ventilation is what I like the most about being oriented with the wind. I open a door on each end, and the wind blows out the hot air. That is less work than having to try to raise roll-up sides for daily venting.

At your latitude, you should orientate your tunnel East and west to maximize your solar gain during daylight hours.

About your gravel, I would skip it. Gravel never stays were you want it. After a few years, or less, you will have gravel in your beds, in the grass around it. Also, thinking long term, if you tear these tunnels out and don't use them then you will have this gravel in the way.

I would instead put a high quality fabric weed barrier around it and run it under the baseboard.

Jay

Professional greenhouses use gravel around there, but they don't plant in the ground of their greenhouses, they use gravel inside also. Plus the gravel will allow you to walk even when it's been very rainy. Gravel does incorporate itself, so you need to put some landscape fabric down first. Gravel is usually lighter color than the landscape fabric, keeping that ground a bit cooler, than just the fabric.

If you are using the fabric, be sure to use the 25 year fabric or the heaviest available. The cheap stuff that you buy easily, will not last.

my east west oriented greenhouse gets hotter quicker than the n-s oriented ones. That is good for spring. But if you're growing in summer, not so good. I move most of my container plants to the n-s ones after spring rush to grow all season.
I will tell you, I hope you don't have the problem I'm having with my greenhouse right next to the hay field. Grasshoppers! they are terrible and eating everything. Even inside the greenhouse. We have a lot more praying mantis now, but they aren't keeping up. I'm getting ready to screen the sides of my greenhouse so they won't get in when they're rolled up.

Thanks for the answers. I will get the weed barrier for sure then. I guess E-W orientation would work best for solar gain in my climate. The wind would then strike them obliquely - is this an issue?

We were very nervous about strong winds. I read that the important thing is to make sure the tunnel is closed up. Due to worry about snow and ice, my husband chose a typical cape cod style roof/wood frame construction. The snow usually slides off, even on the north side but it is also brushed off. You don't want wind to get inside that might lift the structure. We had a 10' long portable low tunnel covered in Agribon fabric blow across the field and over a stone wall.

We have only been thru one winter. I noticed that I have earthworms in the beds on the north side but none in the beds on the south side. Temps got over 100 F even with the sides rolled up. One have a double door on one side (west) that is left open during the summer.