Its the "transfer to lake and back" part that is the real killer here.
To be of any value I would say that the slider needs to be at least 20 feet long. I have a 30 foot slider and your barely on it before you are dismounting. I would think that anything shorter than that you will be bouncing off it rather than sliding it.
Hauling something that is 20 to 30 feet long will require a trailer. This will also mean that you will need two tow vehicles: one for the boat and one for the slider.
Moving the slider down the road is easy enough, moving the slider from the launch ramp to the spot you want to use it will be a bitch. Unless you spend a lot of time & expense designing a slider that has a hull shape for towing purposes moving it through the water will probably need to be done at idle speed.
To be portable it will probably need to be a floating slider. It will need to have enough floatation so that it doesn't sink when you hit it. It will also need to have a wide enough base so that it doesn't tip over when you hit it a little off center or at an angle. This wide base needs to be made in such a way that it won't kill someone who manages to fall off the rail and crash into the base.
Anchoring the slider is non-trivial. If the water is shallow and the bottom a nice soft mud or sand an anchor will hold really well. If the bottom is hard rock and/or more than 20 feet deep the slider will be moving around a lot on you.
Floating sliders move and rock quite a bit when they are getting hit with a lot of wakes. Such a moving target can be a lot harder to hit than a stationary slider fixed to the bottom.
The slider I have is an inflatable 30 foot model that was made by Rave Sports. They don't make them any more but you can occasionally find a used one that is still in serviceable condition. Mine is about 6 years old and still doing fine.
I anchor mine in a shallow protected cove that is too small an area to be of interest to wakeboarding or other similar sports. I use my inflatable dinghy to pull with so it makes a trivial wake and I can turn really sharp. Getting a rider up wiht only 9.9 Hp is a bit of a trick......
If you want to see an example of our slider in use go look here:
http://rodm7.tripod.com/ I carry that mostly assembled on the top of our houseboat. To deploy I need to hoist the slider over the side, install the two end ramps, tow it out to the desired spot, drop two anchors, adjust the lines. This process will take about an hour. Getting the slider back aboard the houseboat is the reverse of the process, takes another hour.
Rod