It definitely needs longer bunks, I like mine to stick out the back past the transom at least 6". I made my own guides but they really aren't needed. My trailer similar to that and what I do is back in the water to the point where the tires are just about submerged, the weight of the motor and fuel tank make the boat slighly tail heavy so it tips rearward as it slides back. Some silicone spray o the carpet does wonders for getting it to slide but a light boat should be an issue.
Mine will slide into the water once its about 3ft back from the winch post.
For loading, I don't go in as deep, I only wet about 3ft of the end of the bunks. I then drive onto the trailer and give the motor a bit of a push to stick the boat. It'll push about half way onto the trailer that way.
I put an eye hook on right side of the trailer atop the side guide that lets me reach down and grab the winch cable so I can clip it on to the bow before getting out of the boat. I also have an electric winch on a remote control so I can pull the boat fully into place from inside my boat if I wish but rarely is it needed. I can usually just grab the cable and pull the boat up myself just by pulling on the cable a bit.
If your having trouble getting the boat to stay on the bunks, your in too deep and/or the bunks are too short.
A front roller can help but only if your dealing with a heavier boat, most small boats don't weigh but a few hundred pounds plus the motor and fuel weight.
Once the boat is 2/3rds of the way on it should sit flat on the bunks and not be trying to flip backwards off the bunks.
On my trailers, the axles are fairly far forward mainly because we have a bunch of ramps that have sharp drop offs at the end not that far into the water. A trailer with a set back axle can drop off the edge before the boat hits the water at a few ramps.
I only take my 14ft boat that 's on a tilt trailer to the one lake because its impossible to back in deep enough to float the boat. The far end of the ramp is only about a 18" deep or so.
Many of the newer ramps are made this way.
My truck's front tires will be 4ft from the top of the ramp in 3" of water and the bottom of the boat's stern will not yet be wet. The ramp goes out 18ft into the water then drops off to 5ft all at once. with the boat trailer tires at the edge, most boats are not yet floating. A tilt trailer is a must. What I do there is to not use the ramp at all, I back up the edge of the water next to the ramp, pull the tilt pin and just dump the boat in. To unload I tilt the trailer and winch it out.
