you should try running a bleach gel. It denatures the RNA without heat, urea, formaldehyde, etc. It also takes care of RNases. The bleach (6.15% hypochlorite) only needs to be added to the agarose in solution, not the buffers.  It's 1% bleach (v/v, so 500uL in 50mL buffer, my lab uses TAE) into your 1% agarose solution, incubate at room temp. for 5min with occasional swirling, then you heat as usual, add ethidium bromide or whatever your lab uses, then pour and allow to set as usual.

The only thing you need to do to your samples is add load dye. From my experience this is a reliable procedure that yields clear bands (28S, 18S and even 5.8S)

Here's a link to the paper we got this protocol from:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3699176/

A commom protocol for RNA electrophoresis is the use of 5% formaldehyde in 1x MOPS buffer. I also add ethidium bromide into the 1% agarose solution. Have you ever tried?

If possible, do not forget to you DEPC water in all solutions.

Here is a promega protocol: https://www.promega.com.br/resources/pubhub/enotes/what-type-of-analytical-agarose-gel-do-i-need-for-my-rna-samples/

You can also have a look in Maniats (http://www.molecularcloning.com/). It is a great book!

If you are running a denaturing gel for RNA you can use this protocol also. Make 1% agarose gel in TBE (which is made in DEPC treated water). Everything you use should be DEPC treated. Also wash your apparatus with 1% SDS. Weak band may be because of RNase contamination.

Make sample Loading buffer containing 90% formamide, 20mM EDTA, 0.05% SDS, 0.025% BPB, 0.025% XC. just add equal volumes of the buffer to your sample and heat at 65 degrees for 5 minutes and quickly load on the gel. formamide solves the problem of band diffusion.

Also add Ethidium bromide to your gel if you dont have to proceed for northern blotting. if you have to proceed for northern blotting dont add EtBr as it will interfere with the membrane. Good luck!