It's with great pleasure and pride that I provide you with a homemade AKA 'one off design' for what I'm describing.
Remove the red screw (incorrectly labeled a bolt) turn 180 degrees, move the mudguard bracket (in green) to the inside of the chainstay and reinsert the screw.
My only concern would be that if the screw is too long it'll come out too far so it'll interfere with the trailer mount. XRHYGYGDGDFS's picture has this issue. It's a 2 min fix to shorten the bolt if you have the right kit, or know a friendly engineer that you can flatter into shortening the screw.
If that's a problem; does the either the carrier bolt or the mudguard bolt have enough spare length to take both the carrier and the mudguard brackets on one mount? The one furthest away from the axle ofc

. Getting new screws should be a case of a visit to your nearest friendly hardware shop. It's easier to get a new bolt that's longer then getting the old bolt cut down unless you have the tools.
I really need to install a better image editor.
As a related aside : With any vehicle you need to be doubly sure your brakes are in fine fettle when pulling a trailer. It's not the pulling, it's the stopping you see