big gap between layers after sliced

I was getting a similar problem using Slic3r. I think the problem is with the model itself, but Slic3r seemed particularly prone to the problem. I switched to Cura (still using RH) with the same model and it sliced correctly with no gaps. I probably should have looked at the model and repaired it, but as it worked fine with Cura (which I also prefer for various other reasons) I just left the model alone and switched to Cura permanently.

Netfabb is your friend!

I agree with wardjr, if you have a bad model of slic3r, nothing should slice right. So check on your model and see how that works

No question that if Cura can cope with a faulty model than it is a viable solution.  Many of the models downloaded from Thingiverse are not printable models.  The reason Slic3r is having problems slicing it though is because the model either isn't manifold or one of the parameters in your profile doesn't match the requirements of the model.  For example there may be an area that is thinner than the set extrusion width in your profile.  So what I am saying is both slicers are capable of slicing the model if it's manifold.  But, because Slic3r offers more control over how the object gets scanned you need to understand the cause of an error.  Cura simply has the profile set up differently allowing it to slice properly.
Under any circumstance Net fabb is a highly regarded tool and should be utilized by every user.  You maybe don't need it today but you will eventually need it.  So in an effort to help you both become better and smarter I would suggest you take a little time to experiment.  See if you can find the cause of the issue and correct it.  I am happy to assist in any way I can.

As always Happy Printing