Hello, I'm interested in 4wd camper rental in Alice Springs, the only company I could find is http://www.wickedcampers.com.au/locations/northern-territory/alice-springs.html
I've found poor opinions about them, do you have any experience with that company? Or maybe you could recommend something. Thanks a lot for opinions/tips

Welcome to the forum.
Wicked does indeed have a poor reputation for when there are problems - usually associated with breakdowns, lack of support, and lack of refunds. Their vehicles are cheap.
Why do you need a 4WD camper ... where are you planning to travel?

Thanks for response. That is only because I want to take Mereenie Loop. As I've read other cars can't go there (no insurance coverage, penalties)
If you search on 4wd camper hire alice springs, there seems to be a lot of companies. This is a fairly big tourism industry in Alice Springs. Mereenie Loop is good ... need to get a permit from the Central Land Council, and other outlets.
Sometimes reputations grow and even in the wrong direction and in the case of Wicked, their reputation has grown because they are cheap and have campervans with stand out paint schemes coupled with some controversial sexist slogans, to the extent that some local government councils would like to ban them and Queensland has even done something about it though that could be moot if a vehicle is registered in another state.
They are not the only cheaper rental company and are still operating after quite a few years and quite a few of their campervans seem to be getting a bit younger. You might find that their 4WDs on offer are the Mitsubishi Delica which come in a 4WD configuration, they being a mini campervan as against your usual wagon shaped 4WD but the good news is that Mitsubishi are a decent enough make and plenty of Delicas about.
The other good news is that they'll likely be cheaper than anything else you find and the chances of a breakdown on a shorter hire are reasonably small.
The bad news is that you might score a paint scheme that even the camels are horrified of.

The following web sites cover a range of hire companies and have 4WD camping type vehicles -
http://www.ecampervanhire.com/
http://www.drivenow.com.au/home/campervan-hire
You will struggle to get a traditional campervan (i.e. kitchen and sleep inside) in 4WD, rather typically they will be standard 4WD set up for camping with a tent etc.
Bear in mind the Meerinie Loop itself is only 100km and about double that distance between Glen Helen and Kings Canyon so you could do this leg in a day and therefore stay in normal accommodation.
Be forwarned that a number of the campervan hire companies have a base hire rate that includes an excess damage component. The excess for some campervans (such as Britz) can be $5,000 to $8,500. This means that if you damage the vehicle you pay the excess. All hire companies have an option for an additional charge where you can waiver some or all of the excess which can add quite a lot to the hire cost. Some premium credit cards and travel insurance policies have an excess car hire insurance component or you can take out car hire excess insurance yourself (which is often cheaper than what the hire company will offer).
You also need to be aware that for campervan hire they require a security deposit where they will pre debit the excess damage cover from your credit card BEFORE you take the campervan. This means for say a $7,000 excess you need the $7,000 credit available on your card and you will not be able to use this credit while you have the van. And if you have taken out excess insurance separately this pre debit still applies!
2WD vehicles including campervans will restrict use to sealed/bitumen roads (often with restrictions on night time driving).
So you need to check the fine print i.e. the hiring conditions, BEFORE you sign up.
Wicked Campers have a bad reputation and it’s not just their appalling looks (very bad taste slogans plastered on the body work). They seem to be prone to breakdowns and very poor on road breakdown service. And in the middle of the Meerenie Loop wouldn’t be a good place to breakdown!
Yes ... if you leave Kings Canyon very early, you can have a fabulous day driving through to Glen Helen Gorge (a lovely place to stay as well), using the Mereenie Road or an alternative route. The Google Map says around eight hours for each.
After Glen Helen, the (sealed) drive back into Alice Springs is one of the best inland day-trips in the country - it is outstanding. Places like Ormiston Gorge, Ellery Creek Big Hole, Simpson's Gap.
So the point is well made above - perhaps you can do this all more easily with a simple 4WD vehicle and either camp or hostel at Kings Canyon and Glen Helen.
Depends on the rest of your plans too, of course ... there are a number of other very good day-trips from Alice Springs that require 4WD (Palm Valley, Rainbow Valley, Chamber's Pillar, East MacDonnell's, etc).