Can we travel with fresh tank full? We lose half on the way.

Mine will do that. Do you have a hose that goes back up to the gravity fill spout? On this trailer and my previous one they just put in the vent tube and left it, no hose! So the sloshing would always be spilling out water. With my previous trailer I bought a piece of clear hose and ran it from the overflow/vent to the vent at the gravity fill. Never lost any water after that. On my current one I haven't done it because I don't need anymore than 5-7 gallons for a couple of flushes and hand washing. If I need to I fill up when I get to where I'm going.

Never heard of it before this post. Something I will have to look for if I switch from Northwood, their vent is up where you fill.

I have the same issue with my Class A motorhome. The overflow/vent outlet is poorly located on the side. I lose a lot of water in transit, when I make a left turn and when I am on an incline that makes the water flow to the passenger side. I modified the routing of the overflow/vent line. It helped some, but I still lose too much water. I think what I really need to do is take the tank out and relocate the overflow/vent outlet to the top-center of the tank. I've got to do a little research, but it doesn't look like it will be that difficult.

I've attached my before and after pics.

Make the vent tube a big S that may stop it

I put a ball valve on my over flow tube . .as soon as I get to the campground , it gets opened up with no loss of water..

Once that siphon starts , its hard to stop it.

I lose little (if any) fresh water. But, my fresh tank is beneath the floor (external) so there is a big elevation change between the fill and breather point and the tank on my trailer.

I have seen some trailers lose a little bit on sweeping right handers or big bumps while traveling. But that doesn't mean that the other were not carrying water.

see if you can raise your vent .a few inch,s mite just do it.

I used to lose a lot of water thru the overflow, especially at one campground where you stop to toss the trash on the way out, the right rear was on a low spot but don't think it was near to being half of the tank. I wouldn't plug the vent since it is guaranteed that you will forget to unplug it some time.
bumpy