The thing is, the line will sit on high points along the bottom... you can only slacken the lines so much, but it still looks like tight-ropes between the points and the tow WILL pick up line and bow it if the water is prone to undertow... there's bu&&er all you can do about it.... the clue will be the bobbin slowly pulling up to the blank as long as the line is in the water.... try it and after a few hours pick up the rod and watch where the line enters the water and track it left or right.... it happens
Using a fluoro main-line does help, as most fluoro's take on some water and sink, but they are still susceptible to tow and they will still sit on high points on the bottom.... braided mainlines are worse as the fibres hold air in the weave and float up.... Even sinking braids do this to a greater or lesser degree...
Some folk still use slack lines and I still do at short range, but it's up to you, I'd rather see a take than worry about spooking a fish that's up in the water.....
What you could do, is use a weighted leader (not ideal as they still don't follow bottom contours perfectly) or use a flying back lead and slacken off a tiny bit to ensure that the last 3 feet of your endgame is pinned to the deck, but even that isn't a done deal, as the line will still follow a straight line between two points, but at least it'll be pinned down... ish